This invention relates to the voltage regulator art. Specifically, apparatus is provided for improving the efficiency of a switch mode or switching regulator.
Voltage regulator circuits have been developed for maintaining a constant d.c. voltage supplied to a changing load. Ideally, the voltage regulator should maintain a constant output d.c. voltage for a varying input voltage and a varying load.
Regulator circuits which utilize a series transistor connected between a load and the source of unregulated voltage are well known in the art. A reference voltage is continuously compared with the load voltage and the series transistor is controlled to supply more current when the load voltage is less than the reference voltage. As the load voltage approaches the reference voltage, the series transistor delivers less current.
The series transistor dissipates considerable energy while regulating the load voltage. To reduce this energy consumption, it is possible to operate the series transistor in a switching mode. A switching mode regulator is described in a publication by Motorola Semiconductor Products Inc., No. CER-108, entitled "An Inexpensive Switch Mode Power Supply." The series transistor is forced into full saturation when the load voltage is below a reference voltage, and turned off when the load voltage is substantially equal to the reference voltage. By operating the transistor either fully saturated or turned completely off, the energy consumption of the series regulator transistor is reduced.
The series transistor requires appreciable base current in either type of regulator. The base current is usually supplied by bias resistors. Energy consumption in the bias resistors may be as high as 30 percent of the energy delivered to the load. In order to reduce the amount of energy dissipated by the bias resistors, thereby improving the efficiency of the regulator circuit, an alternate low impedance path for supplying base current is desirable.